Materials Design for Molecular Recognition Devices using Nano-space between tow Oxide Semiconductor Crystals

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By using the STM system, structurally well-controlled CuO-ZnO "open junction" (tunnel junction) is prepared and the effect of the crystal axis orientation relationship at the junction interface on its alcohol sensing properties is discussed. The CuO-ZnO tunnel junctions have atmosphere sensitive electrical properties even at room temperature. When a CuO tip and Zn-terminated polar surface of ZnO (ZnO (Zn-face)) are chosen for making the tunnel junction, the obtained CuO-ZnO(Zn-face) junction shows highly rectifying characters, where CuO-ZnO(O-face) shows not so good rectifying character. Only the CuO-ZnO(Zn-face) tunnel junction shows a pronounced ethanol sensing characteristics. The catalytic active surface of ZnO(Zn-face) would play an important role for the alcohol sensing characteristics of the CuO-ZnO tunnel junction. Through the current studies on the electrical characterization of the tunnel junction between CuO and ZnO, it is appeared that a structurally well-controlled "open interface" having nano-space between two crystals will be appropriate for the chemical sensor elements, which have an ability of molecular recognition.